An MRI isn’t always the best first-choice for diagnosis when patients present with knee pain. While MRI is highly sensitive and it can detect intra-articular pathology, these changes might be associated with degenerative joint disease, which can also be detected by weight-bearing radiographs.
Writing in the September issue of the Journal of the American Academy of Orthopaedic Surgeons, researchers found that in a study of 599 patients 40 years and older, 22 percent were referred by their primary care physician for an MRI and plain radiographic studies were obtained for 58 percent of these patients before the MRI. Only 13 percent had weight-bearing radiographs. Of these patients, 48 percent of MRIs ordered by primary care physicians did not contribute to treatment recommendations. In patients with more than 50 percent loss of joint space, an MRI was considered unnecessary in 95 percent of cases.
Historically plain X-rays of the knee represent the mainstay for diagnosing knee pain. If a clear diagnosis isn’t seen with a traditional X-ray, patients are often referred to a specialist and potentially more advanced imaging, such as a magnetic resonance image (MRI) scans.
While MRI represents a very detailed examination of the joint it is costly and time consuming. A typical MRI costs 12 times as much as a series of plain films. As with other advanced imaging modalities, MRI, in the instance of knee pain, may actually give the clinician too much information. For instance, noticing a small tear in the soft tissue around an arthritic knee joint will not change the treatment plan but may distract from the real pain causing process.
Do pre-referral MRI knee images have any advantage to weight-bearing plain films in diagnosing the cause of knee pain in patients over 40? This study shows that a substantial portion of patients with knee pain present to orthopedic surgery practices having already had an MRI of their knee. It showed that more than half of patients who had significant joint space narrowing seen on weight-bearing plain films had MRI studies that were deemed non-diagnostic by the evaluating physician.
A prior study found that 80 percent of MRI scans ordered by primary care physicians were considered unnecessary by the referral orthopedist.
“Plain radiographic studies can be sufficiently diagnostic of significant osteoarthritis, thus helping to avoid costly MRI studies. Educating physicians on the utility of weight-bearing radiographs, and secondarily, educating patients on the limited indications for MRI, may help to decrease the excessive use of advanced imaging,” the authors wrote.
Limitations of the study
There were several worth noting: This was a single center study, so it is unclear how generalizable the results may be. Second, there was a very strict exclusion criteria which may have led to the underestimation of the number of pre-referral MRIs and an underestimation of the prevalence of arthritis in the study cohort.
Adelani MA, Mall NA, et al. "The Use of MRI in Evaluating Knee Pain in Patients Aged 40 Years and Older," Journal of the American Academy of Orthopaedic Surgeons.2016 Sep;24(9):653-9. doi: 10.5435/JAAOS-D-15-00681.